Questions regarding the ordering of functions

Why does an extroverted function always follow an introverted function and vice-versa? Why does an irrational function allows follow a rational function and vice-versa? I realize that these questions sound elementary in nature, but they have been bothering me for a while and I cannot find any information that adequately answers them.

Because, say your dominant funciton is Ti. Ti represses the feeling funcitons, so your feeling (rational) function can't be your second strongest. You have to chose from eith sensing or intutition. Why would it be extraverted? No sure exactly, but if both of your dominant funciton were either introverted or extraverted, it would be completely unbalanced in that one you are not getting any subjective interpretaion, and the other, you are getting no objective. It would seem impossible to actually live if that was the case. So, if you are Ti, the that can either be supplementated best with Se or Ne.

Within the definitions laid by Jung, the ordering of the functions seem to be somewhat arbitrary. So in other words, the way Model A is set up could very well be completely incorrect.

But there have been theories created around the functions that allows the functional ordering to be part of the definition of the functions themselves.

Binary or dichotomous systems, although regulated by a principle, are among the most artificial arrangements that have ever been invented. -- William Swainson, A Treatise on the Geography and Classification of Animals (1835)